メカニカルアロイングで作製したFe-Cu過飽和固溶体粉末の液相焼結

抄録

Fe-Cu super-saturated solid solution powders were prepared by mechanical alloying of the elemental Fe and Cu powders, and the sintering behavior of the mechanically alloyed powders was investigated in association with the separation behavior of the liquid Cu phase. The chemical compositions of the mechanically alloyed powders were 10∼33 mass%Cu. The powders obtained were very hard in the as-milled state, so that they were subjected to a softening treatment of 1173 K-0.6 ks, and then compacted to test pieces using metallic die. Sintering of the powder compacts was performed at 1373 K which is just above the melting point of copper.
During the ball-milling of Fe-Cu powder mixtures, an extremely large energy is stored within powder particles and single-phase bcc solid solutions are synthesized for the alloys of up to 25 mass%Cu. The large stored energy leads to grain-refining of the (α-Fe+ε-Cu) two-phase structure formed in subsequent softening treatment. In the early stage of sintering, the liquid Cu phase oozes onto the grain boundaries to separate fine γ-Fe grains, and the rearrangement of separated γ-Fe grains results in densification of Fe-Cu powder compacts. For example, an Fe-25 mass%Cu powder compact, in which the liquid Cu phase oozed homogeneously, was densified to 98% in relative density only by sintering treatment, without singnificant coarsening of the microstructure. The sintered material has fine α-Fe grains of less than 20 μm even after sintering of 1373 K-3.6 ks.